1. Field of the Invention
This invention relates to a modulator circuit, particularly though not exclusively for modulating sound signals onto a carrier wave for a video recorder system.
2. Description of Related Art
Video recorder systems commonly use a method of FM modulation for modulating an audio frequency (AF) input signal onto a sub-carrier of the video system. Such FM modulators commonly comprise a resonant circuit, such as an L-C circuit with a variable capacitance provided usually in the form of a varactor diode for modulating the resonant frequency of the circuit. One problem with such circuit is that for hi-fidelity reproduction a relatively large deviation or bandwidth is required (75 Kilohertz), and the simple modulating circuit may well introduce non-linearities.
Another problem which arises is that certain countries, for example France have a television standard requiring amplitude modulation (AM) and therefore a video recorder having an FM modulator would not be suitable for use in such countries.